Electrical signaling apparatus



July 24, 1934. J ROBINSON 1,967,971

ELECTRICAL SIGNALING APPARATUS Filed Feb. 9, 1931 Patented July 24, 1934 UNITED STATES PATENT orrics 1,967,971 ELECTRICAL SIGNALING APPARATUS James Robinson, London, England, assignor, by

mesne assignments, to British Ra'diostat Corporation, Limited, a corporation of Canada Application February 9, 1931, Serial No. 514,599 In Great Britain February 22, 1930 2 Claims. (01.250-20) This invention is for improvements in or relating to electrical signaling apparatus and is concerned with such apparatus for the reception 'of modulated continuous wave-signals (e. g. .te-

5 lephony or telegraphy) transmitted by wireless vide a receiver having alternative means for obtaining the high degree of selectivity and more especially selective means in which any disadvantage of stray effects are readily obviated.

According to the present invention there is provided in apparatus for receiving a carrier wave modulated by a desired signal, the combination with a resonant device comprising a tuning fork tuned for the said carrier wave,

0 electrical driving means operated by the carrier wave signals and electrical driven means controlled by the fork vibrations, and having such high selectivity that there is no response to interfering signals whereof the carrier fre- 5 quency of such interfering signals lies outside the resonance curve of said tuning fork, but differs from'the'frequency of the wanted carrier wave by an-amount less than the highest modulation frequency of the wanted signal,

9 whereby the relative amplitude of different mod- 5 relative amplitude of different modulation freulation frequencies is altered, yet modulations of the carrier wave of the wanted signal corresponding to the whole of the modulation range may be reproduced, of means for altering the quencies in the opposite sense.

Further, according to the present invention there is provided in apparatus for receiving a carrier wave modulated by a desired'signal, the

0 combination with a resonant device comprising 5 high selectivity that there is no response to interfering signals whereof the carrier frequency of such interfering signals lies outside the resonance curve of said tuning fork, but diifers from the frequency of the wanted carrier wave byan amount less than the sum of the highest modulation frequencies of both carrier waves, whereby relative amplitude of difierent modulation frequencies is altered, yet modulations of the carrier wave of the wanted signal corresponding to the whole of the modulation range maybe reproduced, of means for altering the relative amplitude of different modulation frequencies in the opposite sense.

The natural mechanical frequency of vibration of the tuningfork is in most cases arranged to be the same as the electrical frequency of the desired signal-energy, and although the applied electrical energy may include other frequencies, the mechanical vibrating element responds readily to the desired frequency and is 5 little affected by other frequencies. There is thus produced, in the electrical means energized by the mechanical element, electrical oscillations which are only of a frequency equal to the natural frequency of the tuning fork. Also, owing to the low damping of the tuning fork a very close frequency selection, or in other Words, a high degree of selectivity, is obtained.

Moreover, since there is effected a complete change from electrical to mechanical vibration and a second complete change from mechanical vibration back to electrical vibration, it is possible to screen very effectively the one electrical means from the other, and in this way avoid undesired'eifects produced by stray couplings which tend to decrease the overall selectivity of the system.

The electrically operated tuning fork is preferably preceded by one or more electrically tuned circuits which may include amplifying devices. The electrical output obtained from the tuning fork is applied directly or through amplifiers to a rectifier for received signals which may be followed in the usual manner by low or signal frequency magnifiers.

In another form of the invention the received energy may be converted, for example by means of a local oscillator of adjustable frequency, to

a constant frequency and the tuning fork may be employed as a highly selective resonant. device for this constant or intermediate frequency. Thus the mechanically vibrating tuning fork may be usedas a highly selective device in the intermediate frequency stage of a super-heterody e eceiver.

In the accompanying drawing there is shown diagrammatically by way of example, receivers embodying electrically operated tuning forks according to this invention. In the drawing:

Figure 1 is a skeleton diagram of a receiver employing a tuning fork having a resonant frequency equal to the fundamental frequency of the transmission to be received, and

Figure 2 is a skeleton diagram of a receiver of the super-heterodyne type in which an electrically operated tuning fork is employed in the intermediate frequency stage.

Referring to Figure 1, the incoming energy is.

applied to a tuned circuit 10 by, means of. an input coil 11 which may for example-becoupled,

to an aerial system. The tuned circuit 10 is connected to the input of a thermionic-valve12J arranged as an amplifier. A tuning'forlris in this case employed as a coupling between the:-

valve 12 and another thermionic valve 13 operated as a detector. In association with the-tuning fork which is diagrammatically"indicated at 14 there are two electromagnetic coils 15' and 16; The coil l5'is connected in the output circuit of the valve 12 and is eifectiveupon one tine-of the fork and the othertine of the fork is associated with the coil 16 which is tuned by the condenser" 17 and connected to the input side of the valve 13. The valve 13 is coupled by means of a choke capacity-coupling comprising a choke coil 18, coupling condenser 19 and a grid leak resistance 20 to'the input of a magnifying valve 21, and the output circuit of this valve includes terminals 22. A battery 28 or the equivalent is provided for supplying the anode current for the valves and the necessary working" grid biasfor the valves 13 and 21 is applied to the terminals 24 and 25 respectively.

The mechanically vibrating tuning fork 14 is designed to have a resonant frequency equal to the fundamental frequency of the transmission to be received, assuming that the transmission is amplitude-modulated, and the tine associated with the coil 15 is set in motion by the amplified' signalenergy passing through the coil. The other tine of the tuning fork is set in motion accordingly andproduces in the coil 16 electrical variations corresponding with its movement and these electrical variations are applied to the detecting valve 13. The" tuning fork is, as hereinbefore stated, very highly selective and provides the very high order of selectivity set forth in the aforesaid Patents Nos. 1,821,032 and 1,821,033 and susbtantially only the energy of a frequency equal to thenatur-al frequency of the tuning fork produces any effect therein and consequently only energy of this frequency is induced in the coil 16.

Although the tuning fork is very highly selective it is' found that it is responsive to the amplitude variations produced by the signal modulation and passes on these amplitude variations to the coil 16. However, owing to the low damping and/or. high selectivity of the tuning fork, there is aneifect of preferentialtreatment of the lower modulation frequencies with respect to. the higher. modulation. frequencies as described in the aforesaid Patent No. 1,821,032 and: as. stated therein, it can be shown that the amplitude of the signal: response is inversely proportional tothefrequency of the'signal modulation. ltdeans is thereforeprovlded: to correct this frequency distortion inthe receiver now being described and the coupling comprising the choke 18 and condenser 19 is designed to provide this correction.

It is not found readily convenient to construct electrically operated tuning forks for frequencies equal to the higher radio frequencies and in order to avoid this necessity and also to provide a receiver. for receiving any of a plurality of transmissions of difierent basic frequencies, the tuning fork may be employed in-the intermediate stage of a super-heterodyne system. Such a receiver is shown in Figure 2, in whichthere is shown a thermionic valve detector 30 which is connected to a frame aerial 3'11 and to a. local oscillator 32. The detector valve30 is-coupled by means of a tuned anode coupling 33 to an intermediate amplifier of predetermined frequency generally indicated by the reference 34. This amplifier comprises thermionic valves 35 and 36 having a trans former coupling 3'7 of which the secondary coil is-tuned by'a condenser 38.

The valve 16. is coupled by means of the tuning. fork 14 and associated coils 15 and 16 to-a detector valve 39. A chokeecapacity coupling comprising a: choke 43, condenser 44- and leak resistance 48, is provided between the detector valve 39 and magnifying valve 45, the anode circuit of. whichincludes output terminals 46:.

The high. tension supply for the anodes of the valvesv is supplied at the terminal 49 and the necessary working potentialsfor the control electrodes for the several valves. isapplied at the terminals 40, 41 and 42, the negative pole of'the hightension supply and the positivepole of the grid bias supply being connected toth'e cathodes of the valves. and applied at. terminal 47;

In this receiver the, tuning fork 14 is; designed. to resonant at the predetermined intermediate frequency and since distortion is produced by the tuning forkv owing toits. high selectivity and/or low damping, the choke capacity coupling 43, 44 is designed to-correct this distortion.

It is desirable to completely isolate thecoil at one side of the tuning fork from that of the other in order to prevent stray eifects, and for this purpose a screen may be: provided as indicated by the broken line 50 in the drawing. As a further means for avoiding stray effects instead of employing. two electromagnetic coils l5 and 16; one such: coil may be provided at one side of the tuning fork and an electrostatic device at the other side of the tuning fork. Furthermore,- if desired electrostatic devices asso-.- ciated with the tines of the tuning fork may Ice-substituted for both the coils Hand 16,;

It will. also be understood that instead of tun.-

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lie

its

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ing the mechanical vibrating tuning fork to the ,1

rier wave, electrical driving means therefor operated by the modulated carrier wave energy from said collecting means, electrical driven means controlled by the fork vibrations, and means" for converting received signal energy from said electrical driven means to reproduce Wanted modulation frequencies, said device hav at V ing such high selectivity that there is no response to interfering signals whereof the side band frequencies differ from the frequency of the carrier wave of the wanted signals by an amount less than the highest modulation frequency of the wanted signals, whereby the amplitude of wave-form energy corresponding to different Wanted modulation frequencies is varied, yet modulations of the carrier wave of the wanted signal corresponding to the whole of the required modulation range may be reproduced and means for altering the amplitude of waveform energy corresponding to the different wanted modulation frequencies in the opposite sense.

2. A receiver for wave signals including a resonance circuit for wanted incoming signal energy such as is constituted by a modulated carrier wave, a local generator of oscillations of variable frequency, means combining the local oscillations with the incoming energy to produce energy of a constant beat frequency, a tuning fork resonator for this constant beat frequency, electrical driving means for energizing said tuning fork resonator according to said constant beat frequency energy, electrical driven means for received signals energized by the tuning fork vibrations, means for converting the received signals in said electrical driven means to reproduce wanted modulation frequencies, said tuning fork resonator having such high selectivity that the receiver provides no response to interfering modulation signals whereof the side band frequencies differ from the frequency of the wanted carrier wave by an amount less than the highest modulation frequency of the wanted signal, whereby the amplitude of waveform energy corresponding to different wanted modulation frequencies is varied, yet modulations of the carrier wave of the Wanted signal corresponding to the whole of the required modulation range may be reproduced, in combination with means for altering the amplitude of wave-form energy corresponding to the different wanted modulation frequencies in the opposite sense.

JAMES ROBINSON. 

